Proposed here is the purchase of a Thermo Scientific LTQ Orbitrap XL ETD hybrid mass spectrometer equipped with both high-energy collisional dissociation (HCD) and electron transfer dissociation (ETD) capabilities. The instrument will employ an Eksigent Nano Ultra 2D liquid chromatograph for high resolution nanoflow LC separation of complex mixtures of peptides that was recently purchased by the Proteomics Shared Resource. This instrument will be used to support a diverse group of seven major and four minor users that include physician scientists and basic scientists working in five departments, all of whom are extensively NIH-funded. These users were selected from a base of more than 160 principal investigators at Vanderbilt University who have used the Proteomics Shared Resource over the past three years and selected based on their more demanding need for the level of performance afforded by this class of instrumentation. The LTQ Orbitrap XL ETD will be located in the Proteomics Shared Resource, which is one of three centralized MS core facilities operated by the Vanderbilt University Mass Spectrometry Research Center. The instrument will be managed by a team of five professionals in the proteomics core, including the instrument operator and a mass spectrometry engineer, all of whom have specific experience with operation and maintenance of the Orbitrap. Operational funds will come from user fees assessed to investigators and will employ the standard accounting and billing procedures that have been used by the MSRC service cores for several years. An advisory panel will consist of three senior investigators directly representing the users, an ex officio member of Vanderbilt's Office of Research and an independent senior faculty member. The primary uses for ETD on this instrument will be characterization of posttranslational modifications of proteins, studies of protein-DNA crosslinks and identification of protein adducts of reactive metabolites. In addition, the HCD capabilities will enable quantitative proteomics studies using iTRAQ isobaric tagging reagents and other forms of stable isotopic tracer studies, such as SILAC labeling. PUBLIC HEALTH RELEVANCE: The proteomics research community at Vanderbilt University is extensively funded by NIH. More than 160 investigator groups at Vanderbilt University have used the Proteomics Shared Resource since 2006. The Thermo Scientific LTQ Orbitrap XL ETD hybrid mass spectrometer proposed here will bring important new analytical capabilities for characterization of modified proteins and protein adducts that are unavailable with the current equipment in the Shared Resource. Furthermore, this instrument will enable investigators to undertake new experiments, such as quantitative proteomics using iTRAQ reagents that were hitherto impractical with the current instrumentation.